Each pack contain 10 red balls representing, usually, oxygen atoms and the diameter of each atom is 20 mm.

This item is for extending an existing set or for replacing lost parts.

Why do I need these? The single hole means that when used to represent the oxygen in, say, a ketone, or amide, then there are no unsightly holes in the model

The Molymod® system is the original, unique, dual-scale system of high quality low-cost molecular models. These enormously popular sets are ideal for students but are also used by scientists all over the world.